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| Study on the variation ground motion amplification effect of medium-hard free fields with depth under earthquake action |
| LAN Jingyan1，SONG Xijun1，LIU Juan1，2，WANG Yanwei1 |
| (1. Guangxi Key Laboratory of Geomechanics and Geotechnical Engineering，Guilin University of Technology，Guilin，Guangxi 541004，China；2. Institute of Engineering Mechanics，China Earthquake Administration，Harbin，Heilongjiang 150080，China) |
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Abstract The centrifugal model of the medium-hard free field was designed and constructed to be the artificial ground motion observation station. Four group of simulated seismic acceleration records at different depths underground including surface were obtained with gravitational acceleration of 75 g. Nonlinear ground motion effect of soil layer is studied by using the traditional spectral ratio method considering destructive interference，and the vibration mode characteristics of medium-hard free fields ground motion response is analyzed in order to reveals the variation law of the ground motion site amplification effect with depth initially. The results show that the first mode is often the most significant and easy to identify in the field amplification among all modes，but it is not the maximum of all mode amplification factors. In special cases，amplification factor of the first mode is smaller than the other modes. In general，the amplification factor increases with depth. For the second mode and higher modes，the ground motion amplification factor inner of the soil layer is slightly smaller than the surface and base of the soil layer. The amplification factor of the maximum ground motion at the surface appears at 15 Hz– 18 Hz which is in the high frequency band. The ratio of the frequency between the higher mode and the first mode is smaller than the theoretical estimation result，the difference will be increased more with the higher modes.
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2020, Vol. 39 
